Skeletal deformities become evident during the growth of an individual. Often the earliest signs of maxillary or mandibular growth disharmony is dental malalignment. Once recognized, it is possible to guide the growth of segments of the cranio-facial skeleton in order to minimize the need for surgical correction of the deformity.
Maxillary hypoplasia exists in all three dimensions. Transverse deficiency of the maxilla is often treated by the orthodontist with orthopedic palatal expansion. Deficiency in the maxillary in the vertical or anterior-posterior direction has not been satisfactorily cured by non-surgical guided movements because of a lack of a stable or non-mobile anchorage source for orthopedic movements.
Mandibular deficiency can be corrected by functional appliances which position the mandible forward, and presumably allow for posterior condylar appositional growth which stabilizes the mandible in this forward position. Orthodontists employ orthopedic traction in all three dimensions to control or direct the development of a bone to a favorable location.
Cleft palate patients often have transverse, anterior-posterior, and vertical dysplasia. Reconstruction of these patients often involves orthodontic alignment of the segments prior to bone grafting the defects. However, the defects can be large and difficult to manage when the patient is young. The deciduous dentition can also be difficult to manage in regards to orthodontic anchorage preventing definitive alignment of the arches until the patient is in the early teens.
All orthodontic forces adhere to Newton's Law of Reciprocal Forces. If a force is applied to retract, or pull back, a tooth there exists an "equal and opposite" force to move another tooth forward. The resistive value of the posterior teeth is known as anchorage. Orthodontists offset these reciprocal tendencies by using an extraoral force known as a headgear to augment the resistive value of the molar teeth. However, patient compliance may be poor because many patients do not want to wear the headgear, compromising orthodontic therapy and often the final result.
The problem is that the retractive forces are usually continuous, acting 24 hours a day. Realistically most patients will not wear a headgear more than 10-12 hours a day. Therefore, the posterior anchorage is typically fortified 40-50% of the time. All too often inconsistent usage or overt non-compliance reduce this effect even more.
Previous work in this field indicates that endosseous implants can be used to anchor orthodontic forces for tooth movement. These studies indicate that osseointegrated implants have been used to anchor realignment of teeth, without moving the implants. These implants were placed into the bone.
Clinically, hydroxylapatite coated cylindrical implants have been used since July 1984. Solid blocks of dense hydroxylapatite are available for interpositional and onlay grafting of defects during orthognathic surgery. The onlay grafts were used exclusively for cosmetic augmentation of facial defects without carrying loads.
A need exists for obtaining anchorage directly on parts of the jaws in order to allow the orthodontist the capability for moving teeth and bones in any direction. An anchorage device should be small, allow for various parts to fit into it for versatility of use, and be able to fit on bone and be applied to the bone surface only. If the anchorage device requires placement into bone, then it may be difficult to place the device in children because of potential damage to unerupted teeth. In addition, for cranial bone movements for cases of Crouzon's or Apert's syndrome for example, intra-bony devices may interrupt vital structures such as dura or sinusoids.
The objectives of this invention can be stated as follows:
1. It must not enter the bone but should attach to it; PA0 2. it should be relatively thin to lay under soft tissue against bone, without creating significant inflammation; PA0 3. it should have versatility of attachments in order to assume a role for an orthodontic anchor as well as an orthopedic anchor; and PA0 4. it must have sufficient shear strength to absorb chewing forces and forces placed upon it from orthodontic loading.